It is common practice in the construction of liquid cooled internal combustion engines to cast the cylinder block and its water jacket as a single piece. Because the cylinder block and water jacket are one piece, apertures are provided in the walls of the water jacket to permit the removal of sand at the end of the casting procedure. When the engines are assembled, these apertures are then closed with plates or plugs.
It is common practice to insert a “frost plug” into at least one of these apertures. A frost plug is a device which is generally used to determine the liquid level when the contents of a tank are at a temperature below 0° C. The apertures or holes in the water jacket have thus become known as “frost plug apertures”.
It is also known to replace a frost plug with a heating element insertable into a frost plug aperture. Generally, these “frost plug heaters” take the form of a disc-shape body member and have a heating element that extends within the water jacket to keep the engine temperature heated to an acceptable level during cold weather.
In an effort to simplify the process for mounting the frost plug heater onto the engine block and its removal, U.S. Pat. No. 4,851,640 to Smith discloses a frost plug heater that has a cylinder body insertable in a frost plug aperture. The cylinder body is held in place by passing a screw through a bore of the cylinder and securing a yoke to an end of the screw. The head of the screw is located on the outside of the cylinder with the yoke being insertable through the frost plug aperture by tilting the yoke on the screw. Once inserted into the frost plug aperture, the yoke is straightened so that the yoke straddles the aperture with ends of the yoke in contact with the inner circumference of the aperture.
A drawback of this attachment apparatus is that it is difficult for a user to install this frost plug heater quickly given the accuracy required for proper installation and the space constraints of the engine compartment. This is because the yoke has an overall length longer than a diameter of the frost plug aperture and proper tilting of the yoke is required to insert it into the aperture. Installation requires significant manual dexterity of a user and can be very difficult and time consuming depending on the casting wall thickness and the special limitations within the coolant cavity.
The attachment apparatus of the frost plug heater disclosed in Smith also suffers the disadvantage of working loose under engine operating conditions thereby increasing the risk of the frost plug heater falling out of place and causing damage to the engine.
Another frost plug heater is disclosed in U.S. Pat. No. 4,242,564 to Kendall. Kendall also teaches a clamping structure for securing a frost plug heater in a frost plug aperture. The frost plug immersion heater disclosed in Kendall comprises a clamp element having a base engagable against the inner end of the heater body and a pair of channel-shaped clamping arms extending in splayed relation from the sides of the base. A special T-shaped bolt has opposite ends engaging the arms to spread the clamp arms when a nut is threaded on the outer end portion of the T-shaped bolt and is tightened against the outer end of the heater body.
The frost plug heater taught by Kendall suffers the disadvantage of having the nut on the outside of the cylindrical body which makes the frost plug heater body susceptible to loosening by vibration. Also, the nut is exposed to extreme temperature fluctuations and moisture making it susceptible to rust and possible shearing of the bolt leading to failure of the attachment means. This increases the instance of the frost plug heater falling out and causing damage to the engine. Also, because the nut is positioned on the outside of the cylindrical body, the nut and an end portion of the bolt project into the engine compartment. Not only is this a disadvantage from an aesthetic standpoint, but the inability to obtain a “low profile” attachment poses a functional disadvantage where space in an engine compartment is limited.
The attachment mechanism of the frost plug heater of Kendall is also more costly to manufacture from both a materials and labour standpoint as a custom T-shaped bolt is required.